Industrial controllers are special purpose computers used for controlling factory automation devices. Under the direction of a stored program, a processor of the industrial controller examines a series of inputs reflecting the status of a controlled process or device and changes outputs affecting control of the controlled process or device. Generally industrial controllers are constructed in modular fashion to accommodate different applications requiring different numbers and types of input/output (I/O) circuits as is determined by the particular device or process being controlled. The stored control program runs in real-time to provide outputs to the controlled process as electrical signals to outputs such as actuators and the like. The outputs are based on the logic of the control program and inputs received from sensors of the controlled process.
The industrial controller or programmed logic controller (PLC) executes a series of operations that are performed sequentially and repeatedly. In general, the series of operations includes an input scan, a program scan and an output scan. During the input scan the PLC examines the on or off state of the external inputs and saves these states temporarily in memory (e.g., a file). During the program scan the PLC scans the instruction of the program and uses the input status to determine if an output will be energized. The output results are then saved to memory (e.g., a file). During the output scan the controller will energize or de-energize the outputs based on the output results stored in memory to control the external devices.
A conventional language for programming the stored program is relay ladder logic. Each ladder logic program comprises one or more ladder logic statements, referred to as rungs or instructions. The ladder logic statements define relationships between an output variable and one or more input variables. Input variables are variables that correspond to signals at input terminals and output variables are variables that correspond to signals at output terminals. In relay ladder logic, the input and output signals may be represented graphically as contact symbols and coil symbols arranged in a series of rungs spanning a pair of vertical power rails. A typical ladder logic statement may indicate that a specific output variable is “on” if and only if a first and a second input is “on”.
The ladder logic program not only manipulates single-bit input and output data representing the state of the sensing and operating devices, but also performs arithmetic operations, timing and counting functions and more complex processing operations. A ladder program can be created by connecting a special input module to a PLC that includes a small keyboard and entering ladder logic statements directly into the memory of the PLC. Another method of creating a ladder logic program involves, utilizing a ladder logic program development/editor tool residing on a separate device, such as a personal computer. An operator or programmer of the personal computer draws a series of ladder logic graphs representing each rung or instruction directly on the computer display screen. Once the ladder logic program is complete, the PC software converts the graphs into the corresponding ladder logic commands. The ladder logic command are then transferred to the PLC and stored in the PLC memory.
A PLC and/or a personal computer device can store one or more ladder logic programs and versions. However, a user must manually upload and download ladder logic programs at a work station or personal computer running a developer/editor application program. The current program running on the industrial controller can only be selected and/or changed by the editor. Data backup, storage and trend data is invoked through an application program and stored on a RAM residing on the industrial controller. The size of the RAM is limited and can eventually overload. An operator must periodically upload the data to remove it from the industrial controller memory to avoid overloading. Additionally, a program may include different profiles (e.g., different recipes) and associated parameters regarding particular implementations of a process. Conventionally, these different profiles are stored in huge dimensional arrays within the application program utilizing the memory of the industrial controller.